Foamed synthetic resins such as rigid polyurethane foams (hereinafter, also referred to simply as rigid foams) have been widely produced by reacting a polyol and a polyisocyanate and foaming the mixture in the presence of a foam stabilizer, a catalyst, and a foaming agent.
A spraying method is frequently used in production of rigid polyurethane foams that are used, for example, as a heat insulator particularly in construction sites.
The spraying method is a method of forming a heat insulator or the like by feeding a raw material liquid under high pressure, spraying the raw material liquid for example onto a wall to be coated through a spray gun, and foaming the liquid instantaneously on the wall. Various studies on the spraying method have been made to produce high-quality rigid foams (e.g., Japanese Patent No. 5504877, Re-publication of PCT International Publication No. 2013/058341, and Japanese Unexamined Patent Application Publication No. 2015-4011).
Patent Document 1 (Japanese Patent No. 5504877) teaches that, for improvement of the storage stability of a blended polyol raw material to be foamed only with water, the content of terminal oxyethylene block chains of the polyether polyol is preferably adjusted to 5 to 15 mass % in the total amount of the alkylene oxides.
Patent Document 2 (Re-publication of PCT International Publication No. 2013/058341) teaches that, for improvement of the storage stability of a blended polyol raw material to be foamed only with water, the polyether polyol preferably has random polymerization chains of oxyethylene and oxypropyl groups and the content of the oxyethylene group is preferably adjusted to 20 to 60 mass % in the total amount of the alkylene oxides.
Patent Document 3 (Japanese Unexamined Patent Application Publication No. 2015-4011) teaches that, for production of high-quality rigid foams, the amount of the Mannich polyol used is preferably adjusted to 45 to 80 wt parts.
However, the storage stability of the blended polyol raw material is still unsatisfactory and further improvement is desired. Especially, storage stability in high temperature range (e.g., 40 to 50° C.), which may be encountered in summer time, is desired.